1. Field of the Invention
The present invention relates to a mobile machine arrangement for excavating ballast from a ballast bed including a central portion supporting a railroad track and a respective shoulder portion at each side of the track, for cleaning the excavated ballast and for redistributing the cleaned ballast to the ballast bed, which comprises at least one machine frame supported on undercarriages for mobility on the track in an operating direction, a ballast excavating chain including a transverse course insertable in the central ballast bed portion under the track for excavating ballast from the central ballast bed portion and an ascending course for conveying the excavated ballast, a first ballast cleaning screen arranged to receive the conveyed ballast from the ascending course of the ballast excavating chain and to separate the ballast into a cleaned portion and a waste portion, a ballast excavating device preceding the ballast excavating chain in the operating direction at each side of the track for excavating ballast from each ballast bed shoulder portion and for conveying the excavated shoulder ballast, a second ballast cleaning screen arranged to receive the conveyed shoulder ballast from the ballast excavating devices and to separate the ballast into a cleaned portion and a waste portion, ballast conveyor means for redistributing the cleaned ballast portions and for removing the waste portions.
2. Description of the Prior Art
During the last few years, the cleaning and rehabilitation of railroad track supporting ballast beds has become more difficult not only because the rehabilitation work requires train traffic to be stopped and thus to interrupt the ever more frequent schedules but also because economical considerations make it desirable to clean not only the upper ballast layer but at the same time to clean the entire ballast bed down to the subgrade in a single operation while the track is lifted. This considerably increases the amount of ballast that must be handled by the machine and correspondingly decreases the output, i.e. the speed of advance, of such ballast cleaning machines.
In substance, rehabilitation of the railroad track ballast bed comprises excavating the dirty or encrusted ballast, cleaning the excavated ballast, returning and redistributing the cleaned ballast, and conveying the waste away from the rehabilitation site. This has been done with mobile ballast cleaning machines of the above-described type. The transverse course of the ballast excavating chain extending under the raised track generally excavates the ballast across the entire ballast bed width in a single pass, which forces the machine to advance only very slowly even if its maximal operating capacity is used. The forward speed of the machine decreases in proportion to the depth of excavation, i.e. the amount of ballast being excavated. Furthermore, because of the very inconvenient train traffic interruption caused by the track rehabilitation work, the work is performed relatively rarely so that the ballast becomes heavily encrusted, preventing drainage and making the ballast cleaning more difficult. It has been proposed to facilitate drainage without cleaning the ballast along the entire ballast bed width by using shoulder ballast cleaning machines using shoulder ballast excavating devices at each side of the track. Such machines work at a forward speed somewhat exceeding that of mobile ballast cleaning machines designed to recondition the ballast along the entire width of the ballast bed.
U.S. Pat. No. 4,538,687, dated Sept. 3, 1985, discloses a mobile ballast cleaning machine designed to excavate ballast along the entire width of the ballast bed and, to increase its output, the machine is equipped with a double ballast cleaning screen and an auxiliary conveying chain for conveying the excavated ballast from the transverse course of the ballast excavating chain extending under the raised track to the screen. This makes it possible to clean a larger volume of ballast at an increased forward speed of the machine. A track lifting device is arranged immediately adjacent the transverse excavating chain course and the excavated ballast is conveyed to the double ballast cleaning screen arrangement by the ascending course of the chain and by the auxiliary conveying chain, thus greatly increasing the capacity of the machine. The transverse excavating chain course excavates and conveys the dirty ballast to the shoulder while creating an excavated ballast bed gap under the raised track, and the ascending excavating chain course and the auxiliary conveying chain convey the excavated ballast to the ballast cleaning screen arrangement. During the ballast reconditioning operation and forward movement of the machine, the track is continuously raised so that it is possible to use an excavating chain of a larger or smaller operating height under the track, depending on the desired depth of excavation. The cleaned portion of the ballast is conveyed from the double ballast cleaning screen arrangement and redistributed immediately behind the transverse excavating chain course in the excavated ballast bed gap while the waste portion is conveyed from the screen arrangement by a conveyor arrangement to freight cars preceding the mobile ballast cleaning machine in the operating direction. This machine has been successfully used and provides high-efficiency recondititioning of a ballast bed.
British patent No. 970,010, published Sept. 16, 1964, discloses a mobile ballast cleaning machine arrangement comprising two machines coupled to each other for common movement in an operating direction, each machine comprising a machine frame supported on two undercarriages with a relatively short wheel base, the leading machine being equipped with two shoulder ballast excavating devices with an associated ballast cleaning screen and the trailing machine being equipped with a ballast excavating chain having a transverse chain course insertable under the track and an associated ballast cleaning screen, and each machine also having conveyor means for redistributing the cleaned ballast and for removing the waste from the respective ballast cleaning screens. This machine arrangement, which has no track lifting means, enables the ballast from the center portion and the shoulder portions of the ballast bed to be excavated and cleaned in a single pass, and a common conveyor band enables the redistributing means on the trailing machine to redistribute the cleaned ballast in the ballast bed gap excavated by the transverse ballast excavating chain course. When the shoulder ballast excavating machine is used alone, the excavated shoulder ballast is cleaned and the cleaned ballast is redistributed by discharge chutes at the same shoulder. When the machines are coupled together, the forward speed of the machine arrangement is quite slow.
U.S. Pat. No. 4,705,115, dated Nov. 10, 1987, discloses a structurally complex mobile ballast reconditioning machine with two shoulder ballast excavating ditcher wheels preceding a relatively wide undercutter revolving in a transverse plane extending vertically with respect to the track axis for excavating ballast from beneath the track. The relatively large ditcher wheels excavate the shoulder ballast and convey it up to a level extending at about half the height of the machine whence it is conveyed across the rails towards the center of the track by transversely extending conveyor bands and thence by conveyor bands extending in the track direction across the endless undercutter chain to be discharged immediately behind the undercutter on the center portion of the ballast bed without being cleaned. The ballast excavated by the undercutter is conveyed to a ballast screen cleaner and the cleaned ballast is discharged in the excavated track shoulders. In other words, only the ballast from the center portion of the ballast bed beneath a track which is not raised is cleaned with this machine while the shoulder ballast excavated by relatively complex bucket conveyors and conveyed by cumbersome conveyor arrangements is redistributed to the center portion of the ballast bed without being cleaned.
Finally, an article in "Railway Track & Structures", October 1987, pages 17, 18, 20 and 21, discloses a ballast cleaning system comprised of two independently movable ballast cleaning machines. The leading machine is one according to U.S. Pat. No. 4,705,115, with two shoulder ballast excavating ditcher wheels and a centrally arranged ballast cleaning screen. The shoulder ballast excavated by the ditcher wheels is conveyed to the ballast cleaning screen arrangement and is conveyed therefrom to the shoulders for intermediate storage. The cleaned ballast is then received by the two ditcher wheels on the trailing machine, is conveyed across the track rails and back beyond the undercutter on this machine to be deposited below the track, which has not been raised, in the ballast bed gap excavated by the undercutter chain in the center of the ballast bed. The ballast excavated by the undercutter in the center of the ballast bed is cleaned and the cleaned ballast is discharged in the excavated track shoulders. Thus, the two large ditcher wheels with the two transverse conveyor bands and the longitudinally extending conveyor band reaching at half the height of the machine beyond the transversely extending undercutter constitute a device in a mobile ballast cleaning machine for receiving a ballast portion preceding the undercutter and for depositing this ballast portion in the gap of the ballast bed excavated by the undercutter. The entire system is structurally quite complex and requires four large ditcher wheels, two depositions of the cleaned ballast laterally of the track and two complex redistributions thereof, as well as a time-and labor-consuming vertical, transverse and longitudinal ballast conveyance beyond the endless undercutter chain while affording no increase in the efficiency of the machine and its rapid forward movement in view of the fact that the track is not raised during the ballast reconditioning operation.